(a) Field of the Invention
This invention relates to an exposure controlling circuit for electric shutters arranged to start a shutter closing motion with passing a current to a coil (such as of an electromagnet, plunger solenoid or motor).
(B) Description of the Prior Art
An electric shutter of a type made to start a shutter closing motion with passing a current to a coil is known, for example, in U.S. Pat. No. 2,978,970. In this kind of electric shutter, a disadvantage will be produced unless the current source voltage is kept at a value necessary to well drive the coil after the shutter is opened and until a signal for closing the shutter is generated. That is to say, if the voltage of the current source voltage drops to be below a value necessary to well drive the coil in the course of the exposing operation, the shutter closing motion will not be made and the shutter will permanently remain open. This means that not only the film frame exposed then but also the film frame to be wound up later will be all spoiled. Such phenomenon may occur in a general exposure or bulb-exposure and will be likely to occur particularly in the case of a long time exposure.